Predetermined torque release wrench



Sept. 6, i966 E. GRAEOVAC PREDETERMINED TORQUE RELEASE WRENCH 2 Sheets-Sheet 1 Filed July 29, 1964 Sept. 6, 1966 a. GRABovAc PREDETERMINED TORQUE RELEASE WRENCH 2 Sheets-Sheet 2 Filed July 29, 1964 A J/ag fifa/frega* 3,270,594 PREDETERMINED TORQUE RELEASE WRENCH Bosko Grabovac, Altadena, Calif., assignor to Torque Controls, Inc., El Monte, Calif., a corporation of California Filed July 29, 1964, Ser. No. 385,850 5 Claims. (Cl. 81-52.5)

This invention relates to an adjustable torque release wrench of the type characterized by a swingable arm which carries the applied load and which retracts a springpressed pressure member with a snap action when the applied load reaches a preselected magnitude.

It is desirable to provide such a torque wrench that may be used in either rotary direction without the necessity of manipulation for changeover from one rotary direction to another. In most wrenches of this general type, some kind of manipulation is required such as manual adjustment of a reversing mechanism or complete reversal of the position of the wrench itself. Either of these manipulations requires time and attention.

It is also desirable to reduce the cost of such a wrench both by simplification of the structure and by simplication of the assembly procedure. In this regard a typical wrench of this type has a large number of working parts and the assembly cost is relatively high because of the necessity of complicated and tedious assembly and cali- -bration operations.

It is further desirable for long run reduction in cost to increase the durability and service life of such a wrench. In most wrenches of this type the snap action in response to a preselected load involves the sliding of vone metal surface against another under high unit .pressure with consequent concentrated wear that seriously raffects the calibration ofthe wrench.

The present invention meets these requirements by employing a tiltable block or shoe in combination with the swingable arm to retract a spring-loaded pressure member with a snap action when the predetermined magnitude of the applied load is reached. The tiltable shoe is pivotally connected to the end of the swingable arm to avoid sliding frictional contact between the arm and the shoe and, in addition, the shoe fulcrums about one edge on the pressure member when the snap action occurs. Since the fulcrum edge does not shift, frictional sliding action between the two cooperating parts is avoided.

The invention is further characterized by the highly important concept of providing means projecting from the leading face of the pressure member to give the shoe a starting tilt with respect to the leading face of the pressure member. The result of this provision is that the shoe has two opposite normal or starting tilting positions. At each position a central region of the transverse face of the shoe rests against the .projection and one lateral fulcrum edge of the shoe rests against the pressure member.

Which of the two normal starting tilted positions is assumed by the shoe depends upon the direction of the initial load on the swingable arm when the wrench is used for the application of torque. Thus if the direction of the applied load on the swingable arm is initially in the direction of the starting tilt of the shoe, the shoe remains in its starting position; but if the applied force is initially -in the opposite direction the shoe quickly tilts to its opposite starting position early in the application of the load to the swingable arm.

When the load imposed on the swingable arm reaches the predetermined magnitude, the shoe rocks or fulcrums with a snap action in the direction of the initial tilt to a limit position where the shoe tilts against the inner surface `United States Patent O ice Patented Sept. 6,'1966 of the hollow body to the wrench, which inner surface serves as a stop. When the load imposed on the swingable arm is then reduced the shoe returns to its initial tilted position.

By virtue of its pivotal connection with the end of the swingable arm, the shoe cooperates with the swingable arm to constitute a toggle linkage. When the shoe is tilted from its normal tilt in response to an imposed load of the predetermined magnitude, the toggle linkage elongates with a knee action directed laterally against the inner surface of the tool handle with the inner surface serving as a stop. The elongation of the toggle linkage retracts the pressure member in opposition to the spring pressure against the pressure member. lf the initial loading of the swingable arm causes the shoe to rock from one of its normal tilted starting positions to the opposite tilted starting position, the toggle linkage moves past center for knee action in the opposite direction, but the shift past center involves only a slight retraction of the pressure member and it is not confused with the pronounced snap action that occurs when the toggle linkage responds to a load of the selected magnitude.

In addition to minimizing wear, the described toggle linkage arrangement has the highly important advantage of being readily adjustable for use with springs of different spring rates. The adjustment for a particular spring rate is accomplished simply by adjusting the degree to which the central projection protrudes from the leading face of the pressure member. Thus the angle of the starting tilt of the shoe may be varied to match the spring rate of any particular spring that may be selected for use in the wrench.

To'prepare for a production run of a wrench of this type, it is ordinarily necessary to provide a quantity of 'carefully selected uniform pressure springs and, of course,

this requirement makes the springs relatively costly. In contrast, the new wrench construction makes it possible to use springs selected at random since the starting tilt of the shoe may be adjusted to conformto any particular spring rate within a wide tolerance of spring rates.

In the preferred practice of the invention, the projection on the pressure member that determines the starting tilt of the pressure shoe is adjusted by screw action. A further feature of Ithe invention in this regard is that the hollow handle of the wrench and the structural parts therein are designed'to provide a longitudinal passage from the butt end of the wrench through which a tool may be inserted for screw-threaded adjustment of the starting tilt of the shoe. Thus the toggle linkage may be assembled and placed under the pressure of the spring acting against the pressure member before the startin-g tilt is adjusted. Then the calibration of the wrench may be carried out quickly and conveniently.

The features and advantages of the invention may be understood from the following detailed description and the accompanying drawings.

In the drawings, which are to be regarded as merely illustrative FIG. l is a plan view of the presently preferred embodiment ofthe invention;

FIG. 2 is a longitudinal sectional view taken as indicated bythe line 2--2 of FIG. l;

FIG. 3 is a transverse section along the line 3-3 of FIG. 2 showing the construction of a releasable lock employed in adjusting the wrench to respond to different torque loads;

FIG. 4 is an enlarged sectional view taken along the line 4-4 of FIG. 2 showing the tiltable shoe in side elevation with the shoe at one of its two alternate tilted starting positions;

FIG. 5 is a similar view showing how the shoe tilts from the starting position shown in FIG. 4 in response to a load in one torque direction of a predetermined magnitude;

FIG. 6 is a view similar to FIG. 4 showing the shoe at its opposite starting tilted position to respond to a load in the opposite torque direction;

FIG. 7 is a similar view showin-g the shoe tilted from the starting position shown in FIG. 6 in response to a load of a predetermined magnitude in said opposite torque direction; and

FIG. 8 is similar view showing a modilied form of the shoe.

The selected embodiment of the invention includes a hollow body-which forms a tubular shank 10. A wrench head 12 at the working end of .the tubular shank 10 is mounted on the outer end of a relatively long swingable arm 14 that extends into the tubular shank with an intermediate portion of the arm pivotally connected to the tubular shank by a suitable tapered cross pin 15. In the construction shown, the cross pin 15 is permanently confined by a short sleeve 16 that embraces the shank 10 and is suitably permanently bonded thereto.

The wrench head 12 is of conventional construction with a lateral extension 20 of square cross section for releasable engagement with interchangeable conventional socket members. For this purpose, the lateral extension 20 is provided with the usual detent ball 22 under pressure by a concealed spring.

The inner end of the arm 14 is pivotally connected to a shoe 24 to constitute therewith a toggle linkage to increase in length against a pressure member 25 when a load of a predetermined magnitude is applied to the arm, the toggle action involving a lateral knee action. The pressure member 25 is maintained under pressure in the usual manner by a heavy coil spring 26.

In the construction shown, the inner end of the arm 14 is of forked construction to straddle the shoe 24 as shown in FIG. 2, and the end of the arm is arcuately notched as shown in FIG. 4 to straddle and journal a pivot pin 27 that extends through the shoe. The shoe 24 has a transverse face 28 which confronts a leading face 30 of the pressure member 25, and in the construction shown, the leading face is flanked by a pair of tapered wings 32 which confine the shoe.

The pressure member 25 may be mounted in the hollow shank 10 in any suitable manner that permits free axial shift of the pressure member. For this purpose the pressure member may be provided with two spaced circumferential grooves 34 which confine two circumferential series of balls 35 in rolling contact with the inner circumferential surface of the hollow shank.

As heretofore noted, an important feature of the invention is the provision of central means on the pressure member 25 that projects from the leading face 30 thereof to give the shoe 24 a normal starting tilt. In this particular embodiment of the invention, the central means is in the form of a hardened pin 36 that may be regarded as part of the pressure member and is rounded at both ends and is slidingly mounted in an axial bore 38 in the pressure member 25. For the purpose of screw-threaded adjustment of the extent to which the pin 36 projects from the leading face 30, the pin backs against an arcuate seat 40 in an axial set screw 42 in alignment with the pin. The set screw 42 is formed with `a hexagonal socket 43 for the purpose of adjustment.

In the construction shown, the coil spring 26 backs against what may be termed a tubular spring seat 44 with a roller bearing 45 interposed between the springand the tubular spring seat to minimize frictional resistance to rotation of the tubular spring seat. The tubular spring seat 44 Ihas an enlarged portion 46 with an outer screw thread 47 in engagement with an inner screw thread 48 of the hollow wrench body. The tubular spring seat 44 also has an enlarged rear portion 49 which has an outer screw thread 50 in engagement with an inner screw thread 51 of a tubular handle 52. The tubular handle 52 is lrotatably mounted on the wrench shank 10. The tubular spring seat 44 is locked to the tubular handle 52 by means of a locking bushing 54. With the tubular spring seat 44 locked to the tubular handle 52, the pressure exerted by the helical spring 26 against the pressure member 25 may be varied for different torque adjustment by rotation of the handle, such rotation causing axial shift of the tubular spring seat 44 to vary the effective pressure of the spring 26.

In the assembly procedure, the locking bushing 54 is tightened against the rear enlargement 49 of the locking tubular spring seat to lock the tubular spring seat relative to the handle 52. To facilitate manual rotation of the locking bushing 54, it is formed with a hexagonal axial aperture 58 for engagement by an Allen wrench. In like manner the enlarged rear end of the tubular spring seat 44 is provided with a similar hexagonal axial aperture 60 of slightly smaller cross section.

For the purpose of releasably locking the tubular handle 52 at selected positions of rotation relative to the tubular shank 10 of the wrench to hold the helical spring 26 under selected degrees of compression, the tubular shank is provided with a series of circumferentially spaced longitudinal locking grooves 62, there being in this instance, ve such longitudinal grooves equally spaced about the outer circumference of the wrench shank.

For selective cooperation with the locking grooves 62, the tubular handle 52 has an aperture 64 to confine a locking ball 65. The diameter of the locking ball 65 is sufciently greater than the thickness of the tubular handle 52 to extend into the locking grooves 62 selectively for positive engagement therewith. The locking ball 65 is controlled by a knurled locking collar 66. The inner circumference of the locking collar 66 is cut away to provide room for a concealed helical spring 68, one end of which abuts a snap ring 70 and the other end of which abuts an inner circumferential shoulder 72 of the locking collar.

At the normal position of the locking collar 66, with the locking ball 65 confined in its locking position, the helical spring 68 yieldingly holds the locking collar against an index collar 74 on the forward end of the tubular handle 52. When the locking collar 66 is manually axially retracted against the resistance of the helical spring 68, an inner circumferential recess or groove 75 of the locking collar registers with the locking ball 65 to permit the locking ball to retract radially outward from engagement with whichever longitudinal locking groove 62 in which it may be seated. When the tubular handle 52 is rotated to a new rotary position with corresponding shift of the locking ball 65 to a new locking groove 62, the locking collar 66 is released to return to its normal position under the pressure of the helical spring 68 with consequent camming of the locking ball into positive engagement with the new locking groove.

The index collar 74 is mounted on the tubular handle 52 in a manner that permits rotational adjustment relative to the handle in the course of the factory assembly of the wrench. In the construction shown, the index collar 74 has a pair of diametrically opposite set screws 78 that extend into a circumferential groove in the tubular handle. At the time of assembly these two screws are permanently tightened.

In this particular embodiment of the invention, the wrench has -a range of torque adjustment from 0 to 150 inch-pounds and one complete rotation of the handle 52 causes the tubular Spring seat 44 to advance along the inner screw thread 48 of the tubular shank 10 of the wrench for a distance that represents a change of l0 pounds. Thus each of the ve longitudinal locking grooves 62 represents an increment of 2 inch-pounds.

As shown in FIG. 1, the tubular shank 10 of the wrench has a longitudinal index mark 82 which is flanked by staggered lateral scale marks 84. Each of the scale marks 84 represents an advance accomplished by one complete revolution of'the tubular handle 52 and therefore represents a change in torque resistance of inchpounds. The tapered surface 76 of the index collar 74 is provided with a series of ve circumferentially spaced index marks 85 which are numbered 0, 2, 4, 6 and 8. One of these index marks 85 registers with the longitudinal index mark 82 whenever the locking ball 65 is in positive engagement with one of the five longitudinal locking grooves 62 of the shank 10 of the wrench.

A feature of this embodiment of the invention is that the hexagonal aperture 58 of the locking bushing 54 is larger in vcross section than the hexagonal aperture 60 of the tubular spring seat 44 and the hexagonal aperture 60 of the tubular spring seat 44 is larger in cross section than the hexagonal socket 43 of the set screw 42. This arrangement makes it possible to extend a thin Allen wrench through the bushing 54 and the tubular spring seat 44 into the socket 43 of the set screlw 42 to adjust the degree of projection of the pin 36 after the working parts Aof the wrench are assembled. A thicker Allen wrench may be extended through the bushing 54 into the hexagonal aperture 60 of the tubular spring seat 44 to adjust the tubular spring seat without removing the locking bushing. A still thicker Allen wrench may be used for independently rotating the locking bushing 54.

The manner in which the described wrench construction serves its purpose may be readily understood from the foregoing description. The factory calibration of the wrench starts with the locking bushing 54 retracted or removed to leave the tubular spring seat 44 free for rotation. With guidance of a suitable torque-measuring instrument, an Allen wrench is engaged with the hexagonal aperture 60 for rotational adjustment of the tubular spring seat 44 relative to the wrench shank 10 to cause the pressure member to retract against the resistance of the spring 26 when the applied torque is at a relatively low selected magnitude. To hold this adjustment, the locking bushing 54 is tightened against the tubular spring seat 44 by a thicker Allen wrench. y The tubular handle 52 is then rotated to advance the tubular spring seat 44 relative to the wrench shank 10 until the zero index mark on the index collar 74 registers both with the longitudinal index mark 82 and the transverse scale mark 84 0n the wrench shank to indicate a torque of 150 pounds.

With the guidance of the torque-measuring instrument, a thin Allen wrench inserted into the butt end of -the wrench is used to rotate the set screw 42 to make the yielding retraction of the pressure body, i.e. the breaking point of the wrench, occur at exactly l5() inch-pounds. The handle 52 is then 4rotated back to the original lower value for further adjustment. In this way the calibration adjustment is made alternately at the upper and lower ends of the torque scale until the desired calibration is achieved. When satisfactory calibration .has been with the locking bushing 54 tightened against the tubular spring seat 44, the butt end of the rotary handle 10 may be potted, i.e. filled with a potting resin in a well known manner. f

Since the tubular spring seat 44 is advanced and retracted by a relatively course screw thread, it is improbable -that the desired scale mark 85 on the rotary handle 52 will register precisely with the longitudinal index mark 82 on the wrench shank when correct adjustments of the tubular spring seat 44 and the set screw 42 are achieved. It is a simple matter, however, to loosen the two set screws 78 for nal rotational adjustment of the index collar 74 for .precise `registration of the desired index mark 85 on the index collar with the longitudinal index mark 82 on the wrench shank.

As heretofore stated, the degree to which the central means or hardened pin 36 protrudes beyond the leading face of the pressure member 25, determines the angle of the starting tilt of the shoe 24 and this adjustment by means of the set screw 42 is made in accord with whatever spring is selected for a particular wrench. It is apparent that the shoe 24 is bi-stable in -the sense that in the absence of a load on a swingable arm 14 the shoe will remain in whichever of its two alternate starting positions it may be placed.

With the parts positioned as shown in FIG. 4, a rising torque load in one torque direction on the arm 14 tends to swing the arm to the left and also tends to tilt the shoe 24 and when Ithe load reaches the predetermined magnitude, the arm swings to the left to tilt the shoe against the inner circumferential surface 86 of the shank 10 as shown in FIG. 5. When the load is released, the shoe returns to its starting position shown in FIG. 4.

With the parts positioned as shown in FIG. 4, the initial application of a load in the opposite torque direction to the arm 14 swings the arm rightward -to the position shown in FIG. 6, the result being that the shoe 24 is tilted to its alternate starting position. This shift from one of the two alternate tilted starting positions of the shoe 24 is barely noticeable and is -therefore never confused with the snap action of the shoe in response to the rise of the applied load to a predetermined magnitude. With the shoe 24 tilted to the second or alternate starting position shown in FIG. 6, a rising load in said opposite troque direction tends to swing the arm 14 to the right and eventually causes the shoe 24 to tilt with a snap action to its second limit position shown in FIG. 7.

It is apparent that in the described mode of operation, the arm 14 together with the shoe 24 constitutes, in effect, a toggle linkage. In the positions of the par-ts shown in FIGS. 4 and 5, the' shorter arm of the toggle linkage is indicated yby the dotted line 90. On the other hand, when the parts are positioned as shown in FIG. 6, the shorter arm of the toggle linkage is indicated by the dotted line 92. It is apparent that the shoe rfulcrums on its sharp side edges against the leading face 30 of the pressure member 25 without sliding action.

FIG. 8 shows how the shoe may be cut away to permit the shoe to tilt to a greater angle before it is stopped by the inner circumferential surface 86 of the tool shank. In FIG. 8 the shoe 24a is cut away to provide two opposite inclined edges 94 and 9S which swing against the inner circumferential surface 86 at the two opposite limit .positions of the shoe.

My description in specific detail of the selected embodiment of the invention will suggest various changes, substitutions and other departures from my disclosure within the spirit and scope of the appended claims.

I claim:

h 1. In a torque wrench having a hollow body and having a work-engaging member rotatably mounted on the body, said work-engaging member being operatively connected to a swingable arm inside the body extending longitudinally of the body, means cooperative with the swingable arm for predetermined resistance to swinging movement of the arm away from a normal position, said cooperative means comprising:

a pressure member mounted inside the body with a leading end directed towards the arm and lfreely movable axially of the body towards and away from the swinging end of the arm, said leading end having a central projection;

spring means urging the pressure member towards the arm; and

a shoe having a transverse face in abutment with both said leading end and said projection thereof the pressure member to receive pressure therefrom,

the shoe being pivotally connected to the arm at the swinging end thereof to constitute therewith a toggle linkage in endwise abutment against the pressure member, the linkage being movable with knee action for longitudinal extension of the linkage to retract the pressure member in response to a load of a predetermined magnitude on the work-engaging memlber,

the hollow vbody conning the knee action of the linkage to limit the tilting of the shoe in response to the load,

the shoe being bistable with two opposite normal starting tilt positions depending on the direction of the initial load on the arm when the wrench applies a torque through the work-engaging member, said Itwo opposite starting tilting positions Ibeing symmetrical with respect to the longitudinal axis of the hollow body, v

said shoe being tiltable from a normal tilt position to a position of greater tilt in response to the load of predetermined magnitude with consequent retraction of the pressure member.

2. A combination as set forth in claim 1 in which said projecting means is adjustable to vary the degree of normal tilt of the shoe.

3. In a torque wrench having a hollow ybody and having a work-engaging member rotatably mounted on the Ibody, said Work-engaging member being operatively connected to a swingable arm inside the body extending longitudinally of the body, means cooperative with the swingable arm for predetermined resistance to swinging movement of the arm away from a normal position, said cooperative means comprising:

a pressure member inside the body with a leading face directed towards the arm, the pressure member being freely movable axially of the body towards and away rfrom the swinging end of the arm;

spring means urging the pressure member towards the arm; `a shoe having a transverse face in abutment with the pressure mem-ber to receive pressure therefrom,

the shoe being pivotally connected to the arm` at the swinging end thereof to constitute therewith a toggle linkage in endwise abutment against the pressure member, the linkage being movable with knee action for longitudinal extension of the linkage to retract the pressure member in response to a load of predetermined magnitude on the work-engaging member, the hollow body confining the linkage to limit the tilting of the shoe in response to the load; and

central means on the pressure member projecting from the leading face thereof against the transverse face of the shoe and giving the shoe a normal tilt, the shoe having two opposite normal tilt positions depending on the direction of the initial load on the arm when the wrench applies a torque through the work-engaging member, v f

the shoe being tiltable from a normal tilt position to a position of greater tilt with-consequent retraction of the pressure member in response to a load of the arm of the predetermined magnitude,

said central means including means in screw engagement with the pressure member for adjustment of the degree of projection of the central means to lvary the normal tilt of the shoe.

4. A combination as set forth in claim 3, which includes an axial passage through the hollow body for access to the central means by a tool for screw threaded adjustment of the central means.

5. In a torque wrench having a hollow body and having a work-engaging member rotatably mounted on the lbody, said work-engaging member being operatively connected to a swingable arm inside the body extending longitudinally of the body, means cooperative with the swingable arm for predetermined resistance to swinging movement of the arm away from a normal position, said cooperative means comprising:

a pressure member mounted inside the body with a leading face directed towards the arm and freely movable axially of the body towards and away from the swinging end of the arm,

said pressure member having a bore therethrough longitudinally thereof;

spring means urging the pressure member towards the arm;

a shoe having a transverse face in abutment with the pressure member to receive pressure therefrom,

the shoe being p-ivotally connected to the arm at the swinging end thereof to constitute therewith a toggle linkage movable with knee action for longitudinal extension of the linkage to retract the pressure member in response to a load of the predetermined magnitude on the work-engaging member,

the hollow body confining the linkage to limit the tilting of the shoe in response to the load;

central means in the bore of the pressure member projecting from the leading face of the pressure member against the transverse face of the shoe and giving the shoe a normal tilt,

the shoe having two normal tilt positions depending on the direction of the initial load on the arm when the wrench applies a torque through the work-engaging member,

the shoe being tiltable from a normal tilt position to a position of greater tilt with consequent retraction of the pressure member in response to a load on an arm of the predetermined magnitude; and

a set screw in threaded engagement with said bore to determine the degree to Which the central means projects from the leading face of the pressure member.

References Cited by the Examiner UNITED STATES PATENTS 2,662,436 12/1953 Harmes 81-52.4 2,789,454 4/ 1957 Woods 81-525 2,934,985 5/1960 Mutolo et al. 81-52.5 2,962,918 12/1960 Hoose 81-525 3,016,773 1/1962 Woods 81-52.4 3,165,014 1/1965 Grabovac 81-52.5

WILLIAM FELDMAN, Primary Examiner. G. WEIDENFELD, Assistant Examiner. 

1. IN A TORQUE WRENCH HAVING A HOLLOW BODY AND HAVING A WORK-ENGAGING MEMBER ROTATABLY MOUNTED ON THE BODY, SAID WORK-ENGAGING MEMBER BEING OPERATIVELY CONNECTED TO A SWINGABLE ARM INSIDE THE BODY EXTENDING LONGITUDINALLY OF THE BODY, MEANS COOPERATIVE WITH THE SWINGABLE ARM FOR PREDETERMINED RESISTANCE TO SWINGING MOVEMENT OF THE ARM AWAY FROM A NORMAL POSITION, SAID COOPERATIVE MEANS COMPRISING: A PRESSURE MEMBER MOUNTED INSIDE THE BODY WITH A LEADING END DIRECTED TOWARDS THE ARM AND FREELY MOVABLE AXIALLY OF THE BODY TOWARDS AND AWAY FROM THE SWINGING END OF THE ARM, SAID LEADING END HAVING A CENTRAL PROJECTION; SPRING MEANS URGING THE PRESSURE MEMBER TOWARDS THE ARM; AND A SHOE HAVING A TRANSVERSE FACE IN ABUTMENT WITH BOTH SAID LEADING END AND SAID PROJECTION THEREOF THE PRESSURE MEMBER TO RECEIVE PRESSURE THEREFROM, THE SHOE BEING PIVOTALLY CONNECTED TO THE ARM AT THE SWINGING END THEREOF TO CONSTITUTE THEREWITH A TOGGLE LINKAGE IN ENDWISE ABUTMENT AGAINST THE PRESSURE MEMBER, THE LINKAGE BEING MOVABLE WITH KNEE ACTION FOR LONGITUDINAL EXTENSION OF THE LINKAGE TO RETRACT THE PRESSURE MEMBER IN RESPONSE TO A LOAD OF A PREDETERMINED MAGNITUDE ON THE WORK-ENGAGING MEMBER, THE HOLLOW BODY CONFINING THE KNEE ACTION OF THE LINKAGE TO LIMIT THE TILTING OF THE SHOE IN RESPONSE TO THE LOAD, THE SHOE BEING BISTABLE WITH TWO OPPOSITE NORMAL STARTING TILT POSITIONS DEPENDING ON THE DIRECTION OF THE INITIAL LOAD ON THE ARM WHEN THE WRENCH APPLIES A TORQUE THROUGH THE WORK-ENGAGING MEMBER, SAID TWO OPPOSITE STARTING TILTING POSITIONS BEING SYMMETRICAL WITH RESPECT TO THE LONGITUDINAL AXIS OF THE HOLLOW BODY, SAID SHOE BEING TILTABLE FROM A NORMAL TILT POSITION TO A POSITION OF GREATER TILT IN RESPONSE TO THE LOAD OF PREDETERMINED MAGNITUDE WITH CONSEQUENT RETRACTION OF THE PRESSURE MEMBER. 